Event recorders are used to measure events, such as operator inputs to a train or other vehicle. Such event recorders are similar to “black boxes” in airplanes. Most on-board event recorders record all of this information into (solid state) memory. Data from the solid-state memory can be uploaded if it must be analyzed or reviewed. Solid-state memory is presently 70 times the cost of hard disk storage; therefore, there is a commercial advantage if hard drives could be used. However, recording technologies for use in rail applications and similar applications must be incredibly rugged.
FIG. 1 shows one approach in which a hard drive 10 is provided within an event recorder data pack 12, for mounting to a mounting surface 14 of a vehicle. The entire event recorder data pack unit 12 including all elements housed within the outer casing is vibration isolated using external vibration isolators 16. External connections 18, which can be rigid or semi-rigid, will also affect the isolation system performance, and the degree of their effect is uncontrollable in that it is dependent on the installation. This approach can be difficult because of the size of the envelope. Also, the vibration isolators to isolate the entire unit from the exterior are expensive.
FIG. 2 shows another approach in which only a hard drive housing 20 is vibration isolated within a hard drive module 28 provided within the outer casing of an event recorder data pack unit 22. Using internal vibration isolators 26, vibration isolation is done internally to the hard drive module chassis. Other environmental control functions can also be performed internal to the hard drive module chassis. This reduces cost, and improves application since, as shown in FIG. 2, the unit 22, or a mobile digital video recorder in which it is mounted, can be bolted directly to a mounting surface 24 of a vehicle. One such approach for using hard disk storage in a mobile event recorder is described in commonly assigned U.S. patent application Ser. No. 11/106,515 filed on Apr. 15, 2005 entitled “Contained Environmental Control System for Mobile Event Data Recorder”, which is incorporated herein by reference. New storage requirements demand the use of multiple hard drives of larger (though fairly standard) physical size and capacity.
Most approaches isolate vibration forces from more than one direction. U.S. Pat. No. 7,234,153 issued on Jun. 19, 2007 to Jensen and is entitled “Vibration Damper for Dampening Vibrations at Low Frequencies”. In this approach, two springs are mutually connected on the same side of a vibration sensitive item to dampen vibration in a way that can compensate for both horizontal and vertical vibration. It is intended to isolate light vibration sensitive elements from a vibration generating base at relatively low frequencies (below 180 Hz). This system does not provide vibration isolation in more than one mounting orientation of the vibration sensitive item.
It can be advantageous to provide a ruggedized environment, including enhanced vibration isolation for more than one hard drive mounting orientation. United States Patent Application Publication No. 2006/0158968 published Jul. 20, 2006 of Vanman et al. is entitled “Method of and System for Mobile Surveillance and Event Recording”. Four silicon oil-filled dampers stabilize the floating mechanism. An oil filled damper can usually only provide damping or isolation in one direction. A spring must be manually pivoted so that it can handle a gravity load in the direction of mounting. It therefore cannot provide multiple orientation vibration isolation without a manual change to the system.
Another known isolator configuration shown in FIG. 3 attempts to deal with vibration in multiple orientations. A hard drive housing 30 including two standard hard drives is isolated within a chassis of a hard drive module 32. Two isolators 34 on the bottom of the hard drive housing 30 are intended to provide isolation, and two further isolators 36 on the right are intended to provide stabilization. However, this approach using two isolators on the side does not permit practical motion because it is too stabilized. This system does not isolate all of the vibrations in various hard drive operable ranges, as they vary based on applied force of vibration, since the natural resonant frequency is too high.
It is, therefore, desirable to provide an improved mobile event data recorder having a vibration isolation system that isolates vibrations in more than one mounting orientation and isolates frequencies in the hard drive operating ranges.